(a) Field of the Invention
The present invention generally relates to the production of trialkoxysilane/tetraalkyoxysilane mixtures in the catalyzed reaction between silicon metal and alcohol. In particular, the present invention relates to the use of mixed solvents to control the ratio of trialkoxysilane to tetraalkyoxysilane in the copper catalyzed reaction between silicon metal and alcohol.
(b) Prior Art
The reaction between silicon metal and alcohol is well established. As long ago as 1949, U.S. Pat. No. 2,473,260 issued to Rochow described a process for the preparation of methyl silicates from methanol and the silicon-copper masses. Similarly, U.S. Pat. No. 3,072,700 taught the preparation of silanes [(RO).sub.3 SiH, (RO).sub.2 SiH.sub.2 ] from silicon metal and alcohol in a fluidized bed reactor.
Patents on the production of tetraalkylorthosilicates include U.S. Pat. No. 4,288,604 and Japanese Patent No. 1979-163529.
Patents covering the production of trialkoxysilane include U.S. Pat. No. 3,775,457. See also Japanese patents 1979-163529, 1980-28929, 1980-28929, 1980-2641, and Japanese laid-open applications 33457/1980 and 11538/1980.
Generally, in the copper catalyzed slurry reaction between silicon metal and alcohol the ratio of trialkoxysilane and tetraalkyoxysilane is not controlled. This is because the reaction of silicon metal and alcohol catalyzed by copper is exothermic and proceeds according to the following equation: ##STR1## The major side reaction proceeds according to the following equation and ##STR2## Tetraalkyoxysilane can also be formed by the secondary reaction of trialkoxysilane and alcohol catalyzed by several materials: ##STR3## Typical materials that catalyze this secondary reaction are: copper, metal chlorides, acids, bases, and metals. Materials like HCl and FeCl.sub.3 are very good catalysts. When cuprous chloride is used as the catalyst, HCl is generated early in the reaction.
Thus, a need exists to control the ratio of trialkoxysilane to tetraalkoxysilane in the copper catalyzed reaction between silicon metal and alcohol.